While performing a white point calibration to a projector, an optical detector is used for detecting light intensities and white balance conditions of red, green and blue light emitting diodes (LEDs) of a light source module of the projector. An application-specific integrated circuit (ASIC) or a digital signal processor (DSP) is used for receiving an electronic signal transformed from an optical signal detected by the optical detector. Thus, corresponding light intensity of the light source module can be measured and used for determining driving current values or duty cycles to apply on the LEDs to optimize the colors of images. Therefore, the choice of the location of the optical detector with respect to the light source module is a critical factor that influences the intensity of the optical signal received by the optical detector and the result of white balance calibration to the projector.
FIG. 1 is a schematic view of a conventional projector 10. FIG. 2 is a schematic view showing an optical detector disposed in the conventional projector 10. An optical detector 11 is directly disposed at a light exit of a light source module 12 and is electrically connected to a circuit board 14. As FIG. 2 shows, the optical detector 11 is disposed above a light entrance surface of an optical integrator 13. Most of light emitted from the light source module 12 is incident into the optical integrator 13 from the light entrance surface, while a part of randomly emitted light from the light source module 12 which does not enter the optical integrator 13 is received by the optical detector 11. After the received optical signals are converted into electronic signals, the electronic signals are transmitted to the signal processor (not shown) through the circuit board 14. Then the signal processor adjusts light intensities and white balance conditions of the light source module 12 according to the electronic signals. However, as the LED packaging technology keeps improving, collimating ability of the light emitted from the light source module 12 is increased. The amount of the randomly emitted light is not enough for the optical detector 11 to receive and corresponding generate electronic signals.
Besides, the optical detector 11 contained inside a sealed housing (not shown) of an optical engine of the projector 10 is close to the high temperature light source module 12. Performance of the optical detector 11 is downgraded as the working temperature of the optical detector 11 is raised. Furthermore, since the optical detector 11 is hung above the light entrance surface of the optical integrator 13 by a supporting member 15, the optical detector 11 may be accidentally tilted from its original position during assembling, causing poor quality of the received optical signal.
Therefore, a problem to be solved is how to properly dispose the optical detector in order to receive signals with better quality and avoiding the influence of the high temperature from the light source module, and correspondingly adjusting the intensity and white balance condition of the light based on the detected results from the optical detector. U.S. Pat. No. 7,168,826 disclosed a projector having a light guiding device, and an optical detector disposed on the light guiding device. U.S. Pat. No. 6,734,957 disclosed an illumination device in a projector, which has an integrating box disposed behind a reflective mirror, and an optoelectronic device disposed inside the integrating box for receiving light. U.S. Pat. No. 7,405,856 disclosed a display system having a light sensor disposed adjacent to an integrating rod. U.S. Pat. No. 8,152,311 disclosed a display apparatus having a light sensor disposed adjacent to a light source. The light sensor can adjust light emitted from the light source according to a detected light intensity.